Conventional resins used in a pultrusion process for making a fiber reinforced resin composite are thermoset resins, such as unsaturated polyester resin and epoxy resins. Phenolic resin which is known to have excellent mechanical properties and electrical properties, especially at elevated temperatures, has been used to produce fiber reinforced products by prepreging, compounding, reaction injection molding or pultrusion processes, but phenolic resin used as a binder in the fabrication of a fiber reinforced composite product so far is still not so popular compared to the others due to its brittle nature which causes its poor coupling with fiber, its slow curing rate, and due to the side product (water) which may be generated causing void defects. Therefore there is a need in the composite industry to improve the quality and properties of a pultruded fiber reinforced phenolic based resin composite.
Several methods have been developed to toughen phenolic resin. For examples, U.S. Pat. No. 2,267,390 uses China wood oil (tung oil), Japanese Patent No. 29-7595 uses rosin, U.S. Pat. No. 2,675,335 uses alkyl phenol, U.S. Pat. No. 4,125,502 uses vinyl acetate and U.S. Pat. No. 4,157,324 uses high ortho etherified resole type phenolic resin for toughening phenolic resin. However, these methods all require the modifying agents to react with phenolic resin for a period of time in order to obtain the desired toughening effect.
At present meta-hydroxyl phenol catalyst is used to shorten the gel time of phenolic resin so that it can be used in manufacturing a fiber reinforced composite product; however, the addition of meta-hydroxyl phenol catalyst also decreases the storage stability of phenolic resin and pot life of phenolic resin.
It is known that the coupling between phenolic resin and the surface of a common fiber is poor, and filaments having a special surface treatment are necessary for the fabrication of a fiber reinforced phenolic resin, e.g. filaments having a special surface treatment by isocyanate based coupling agent are available from the fiber glass manufacturers, e.g. Clark-Schwebel Fiberglass Corp., US, etc. These special treated filaments result in more stocks and production costs, and an additional operation procedure of changing different filaments.
U.S. Pat. No. 5,559,197 discloses a modified phenolic resin which is toughened by phenoxy resin, in which the modified phenolic resin is prepared by the following steps: mixing a phenoxy resin having a weight average molecular weight of 10,000.about.1,000,000 and phenol in a weight ratio of phenoxy resin: phenol=1.5:1.about.1:1 at an elevated temperature to form a glutinous mixture; mixing the glutinous mixture and an acid catalyst to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture; mixing the viscose mixture and a resole type phenolic resin to form a modified phenolic resin, wherein the resole type phenolic resin has a solid content of 60.about.75 wt % and a free aldehyde content of 5.about.10 wt %, the amount of the acid catalyst mixed is 2.about.10 wt %, and the amount of the phenoxy resin mixed is 3.about.25 wt % based on the resole type phenolic resin.
Poly(alkylene oxide) such as poly(ethylene oxide) (PEO) is a high crystalline and water soluble polymer. A suitable method for preparing this polymer includes polymerizing alkylene oxide via a coordination polymerization mechanism catalyzed by an oxide of salt of alkaline earth metal (Ca, Ba and Sr) or a co-catalyst formed by a metallic organo-compound and water. A high molecular weight PEO (10.sup.5 -10.sup.7) is able to be extruded to form a high crystalline solid article. Typical applications of PEO are used as a water soluble packing film, a surfactant, a sizing agent, a gelatining agent, a thickening agent, and a biomedical material, and in preparing an electrically conductive polymer blend.
To our knowledge there is no one in the prior art who taught or suggested using poly(alkylene oxide) to toughen phenolic resin, and enhance the coupling between phenolic resin and fiber at the same time.